Radiation curable ink containing a curable wax

ABSTRACT

Curable monomer that is liquid at 25° C., curable wax and colorant together form a radiation curable ink. This ink may be used to form images by providing the radiation curable ink at a first temperature; applying the radiation curable ink to the substrate to form an image, the substrate being at a second temperature, which is below the first temperature; and exposing the radiation curable ink to radiation to cure the ink.

BACKGROUND

This application is a Divisional of U.S. patent application Ser. No.11/289,615, the disclosure of which is hereby incorporated by referenceherein in its entirety.

The present disclosure generally relates to curable inks, particularlycurable phase change inks, and their use in methods for forming images,particularly their use in ink jet printing.

Ink jetting devices are known in the art, and thus extensive descriptionof such devices is not required herein. As described in U.S. Pat. No.6,547,380, incorporated herein by reference, ink jet printing systemsgenerally are of two types: continuous stream and drop-on-demand. Incontinuous stream ink jet systems, ink is emitted in a continuous streamunder pressure through at least one orifice or nozzle. The stream isperturbed, causing it to break up into droplets at a fixed distance fromthe orifice. At the break-up point, the droplets are charged inaccordance with digital data signals and passed through an electrostaticfield that adjusts the trajectory of each droplet in order to direct itto a gutter for recirculation or a specific location on a recordingmedium. In drop-on-demand systems, a droplet is expelled from an orificedirectly to a position on a recording medium in accordance with digitaldata signals. A droplet is not formed or expelled unless it is to beplaced on the recording medium.

There are at least three types of drop-on-demand ink jet systems. Onetype of drop-on-demand system is a piezoelectric device that has as itsmajor components an ink filled channel or passageway having a nozzle onone end and a piezoelectric transducer near the other end to producepressure pulses. Another type of drop-on-demand system is known asacoustic ink printing. As is known, an acoustic beam exerts a radiationpressure against objects upon which it impinges. Thus, when an acousticbeam impinges on a free surface (i.e., liquid/air interface) of a poolof liquid from beneath, the radiation pressure which it exerts againstthe surface of the pool may reach a sufficiently high level to releaseindividual droplets of liquid from the pool, despite the restrainingforce of surface tension. Focusing the beam on or near the surface ofthe pool intensifies the radiation pressure it exerts for a given amountof input power. Still another type of drop-on-demand system is known asthermal ink jet, or bubble jet, and produces high velocity droplets. Themajor components of this type of drop-on-demand system are an ink filledchannel having a nozzle on one end and a heat generating resistor nearthe nozzle. Printing signals representing digital information originatean electric current pulse in a resistive layer within each inkpassageway near the orifice or nozzle, causing the ink vehicle (usuallywater) in the immediate vicinity to vaporize almost instantaneously andcreate a bubble. The ink at the orifice is forced out as a propelleddroplet as the bubble expands.

In the art, it is known to use phase change inks, also referred to ashot-melt inks. In general, phase change inks are in the solid phase at,for example, ambient temperature, but exist in the liquid phase at theelevated operating temperature of an ink jet printing device. At the jetoperating temperature, droplets of liquid ink are ejected from theprinting device and, when the ink droplets contact the surface of therecording substrate, either directly or via an intermediate heatedtransfer belt or drum, they quickly solidify to form a predeterminedpattern of solidified ink drops.

In a typical design of a piezoelectric ink jet device utilizing phasechange inks printing directly on a substrate or on an intermediatetransfer member, such as the one described in U.S. Pat. No. 5,372,852,incorporated herein by reference, the image is applied by jettingappropriately colored inks during four to eighteen rotations(incremental movements) of a substrate (an image receiving member orintermediate transfer member) with respect to the ink jetting head,i.e., there is a small translation of the printhead with respect to thesubstrate in between each rotation. This approach simplifies theprinthead design, and the small movements ensure good dropletregistration. At the jet operating temperature, droplets of liquid inkare ejected from the printing device and, when the ink droplets contactthe surface of the recording substrate, either directly or via anintermediate heated transfer belt or drum, they quickly solidify to forma predetermined pattern of solidified ink drops.

Hot melt inks typically used with ink jet printers have a wax based inkvehicle, e.g., a crystalline wax. Such solid ink jet inks provide vividcolor images. In typical systems, these crystalline wax inks partiallycool on an intermediate transfer member and are then pressed into theimage receiving medium such as paper. Transfuse spreads the imagedroplet, providing a richer color and lower pile height. The low flow ofthe solid ink also prevents showthrough on the paper.

In these systems, the crystalline wax inks are jetted onto a transfermember, for example, an aluminum drum, at temperatures of approximately130-140° C. The wax based inks are heated to such high temperatures todecrease their viscosity for efficient and proper jetting onto thetransfer member. The transfer member is at approximately 60° C., so thatthe wax will cool sufficiently to solidify or crystallize. As thetransfer member rolls over the recording medium, e.g., paper, the imagecomprised of wax based ink is pressed into the paper.

The images produced with inks composed of crystalline waxes are visuallyappealing; however, lowering the temperature at which the inks arejetted and improving the robustness of the printed images would bebeneficial.

Recently, Xerox has discovered several curable inks that that achievemore robust images following curing. Reference is made to the followingpatent properties, each of which is incorporated herein by reference inits entirety: (1) U.S. Pat. No. 7,270,408, (2) Co-pending U.S. PatentApplication Publication No. 2006/0158492 filed Jan. 14, 2005, (3)Co-pending U.S. Patent Application Publication No. 2006/0158491 filedJan. 14, 2005, (4) U.S. Pat. No. 7,293,868, and (5) U.S. Pat. No.7,459,014.

SUMMARY

The present disclosure describes a radiation curable ink, particularly aradiation curable phase change ink, that can be used in ink jetprinting.

In embodiments, the present disclosure relates to a radiation curableink comprising a curable monomer that is liquid at 25° C., a curablewax, and a colorant. In embodiments, the ink further comprises at leastone radiation activated initiator, specifically a photoinitiator, thatinitiates polymerization of curable components of the ink, specificallyof the curable monomer and the curable wax.

As used herein, the term wax includes natural, modified natural, andsynthetic waxes. A wax is solid at room temperature, specifically at 25°C.

In embodiments, the curable monomer has a viscosity of no more than 20mPa-s, preferably no more than 18 mPa-s, and more preferably no morethan 16 mPa-s at 25° C.

The present disclosure also relates to a method for applying ink to forman image on a substrate. In embodiments, the method comprises providinga radiation curable ink described herein at a first temperature;applying the radiation curable ink to a substrate to form an image, thesubstrate being at a second temperature, which is below the firsttemperature; and exposing the radiation curable ink to radiation to curethe ink. During the curing process, curable components of the ink arepolymerized to form a cured image. In a preferred embodiment, thecomposition is applied over the image by ink jet printing.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE depicts the viscosities of six compositions within thepresent disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

The composition of the present disclosure is a radiation curable ink. Inembodiments, the radiation curable ink comprises a curable monomer thatis liquid at 25° C., a curable wax, and a colorant. In embodiments, thecurable monomer has a viscosity of no more than 20 mPa-s, preferably nomore than 18 mPa-s, and more preferably no more than 16 mPa-s at 25° C.

In embodiments, the ink has a viscosity of from 8 mPa-s to 15 mPa-s,preferably from 10 mPa-s to 12 mPa-s, at a temperature between 60° C.and 100° C. In embodiments, the ink has a viscosity of from 105 to 107mPa-s at a temperature of 50° C. or below, specifically at a temperaturefrom 0° C. to 50° C.

The curable monomer may be any curable monomer that is a liquid at 25°C. In embodiments, the monomer is equipped with one or more curablemoieties, including, but not limited to, acrylates; methacrylates;alkenes; allylic ethers; vinyl ethers; epoxides, such as cycloaliphaticepoxides, aliphatic epoxides, and glycidyl epoxides; oxetanes; and thelike. The monomers are preferably monoacrylates, diacrylates, orpolyfunctional alkoxylated or polyalkoxylated acrylic monomerscomprising one or more di- or tri-acrylates.

Suitable monoacrylates are, for example, cyclohexyl acrylate, 2-ethoxyethyl acrylate, 2-methoxy ethyl acrylate, 2(2-ethoxyethoxy) ethylacrylate, tetrahydrofurfuryl acrylate, octyl acrylate, lauryl acrylate,2-phenoxy ethyl acrylate, tertiary butyl acrylate, glycidyl acrylate,isodecyl acrylate, benzyl acrylate, hexyl acrylate, isooctyl acrylate,isobornyl acrylate, butanediol monoacrylate, octyl decyl acrylate,ethoxylated nonylphenol acrylate, hydroxyethyl acrylate, hydroxyethylmethacrylate, and the like. Suitable polyfunctional alkoxylated orpolyalkoxylated acrylates are, for example, alkoxylated, preferably,ethoxylated, or propoxylated, variants of the following: neopentylglycol diacrylates, butanediol diacrylates, 1,3-butylene glycoldiacrylate, 1,4-butanediol diacrylate, diethylene glycol diacrylate,1,6-hexanediol diacrylate, tetraethylene glycol diacrylate, triethyleneglycol diacrylate, tripropylene glycol diacrylate, propoxylatedneopentyl glycol diacrylate, ethoxylated neopentyl glycol diacrylate,and the like. In the most preferred embodiment, the monomer is apropoxylated neopentyl glycol diacrylate, such as, for example, SR-9003(Sartomer Co., Inc., Exton, Pa.), having the structure:

Suitable reactive monomers are likewise commercially available from, forexample, Sartomer Co., Inc., Henkel Corp., Radcure Specialties, and thelike.

The curable monomer is preferably included in the ink in an amount offrom, for example, about 20 to about 80% by weight of the ink,preferably about 30 to about 70% by weight of the ink, and morepreferably from about 35 to about 60% by weight of the ink.

The curable wax may be any wax component that is miscible with the othercomponents and that will polymerize with the curable monomer to form apolymer. Inclusion of the wax promotes an increase in viscosity of theink as it cools from the jetting temperature.

Suitable examples of waxes include, but are not limited to, those thatare functionalized with curable groups. The curable groups may include,but are not limited to, acrylate, methacrylate, alkene, allylic ether,epoxide and oxetane. These waxes can be synthesized by the reaction of awax equipped with a transformable functional group, such as carboxylicacid or hydroxyl.

Suitable examples of hydroxyl-terminated polyethylene waxes that may befunctionalized with a curable group include, but are not limited to,mixtures of carbon chains with the structure CH₃—(CH₂)_(n)—CH₂OH, wherethere is a mixture of chain lengths, n, where the average chain lengthis preferably in the range of about 16 to about 50, and linear lowmolecular weight polyethylene, of similar average chain length. Suitableexamples of such waxes include, but are not limited to, UNILIN® 350,UNILIN® 425, UNILIN®& 550 and UNILIN® 700 with M_(n) approximately equalto 375, 460, 550 and 700 g/mol, respectively. All of these waxes arecommercially available from Baker-Petrolite. Guerbet alcohols,characterized as 2,2-dialkyl-1-ethanols, are also suitable compounds.Preferred Guerbet alcohols include those containing 16 to 36 carbons,many of which are commercially available from Jarchem Industries Inc.,Newark, N.J. PRIPOLO® 2033 (C-36 dimer diol mixture including isomers ofthe formula

as well as other branched isomers which may include unsaturations andcyclic groups, available from Uniqema, New Castle, Del.; furtherinformation on C₃₆ dimer diols of this type is disclosed in, forexample, “Dimer Acids,” Kirk-Othmer Encyclopedia of Chemical Technology,Vol. 8, 4^(th) Ed. (1992), pp. 223 to 237, the disclosure of which istotally incorporated herein by reference) can also be used. Thesealcohols can be reacted with carboxylic acids equipped with UV curablemoieties to form reactive esters. Examples of these acids include, butare not limited to, acrylic and methacrylic acids, available fromSigma-Aldrich Co. Particularly preferred curable monomers includeacrylates of UNILIN® 350, UNILIN® 425, UNILIN® 550 and UNILIN® 700.

Suitable examples of carboxylic acid-terminated polyethylene waxes thatmay be functionalized with a curable group include, but are not limitedto, mixtures of carbon chains with the structure CH₃—(CH₂)_(n)—COOH,where there is a mixture of chain lengths, n, where the average chainlength is preferably in the range of about 16 to about 50, and linearlow molecular weight polyethylene, of similar average chain length.Suitable examples of such waxes include, but are not limited to, UNICID®350, UNICID® 425, UNICID® 550 and UNICID® 700 with M_(n) equal toapproximately 390, 475, 565 and 720 g/mol, respectively. Other suitablewaxes have a structure CH₃—(CH₂)_(n)—COOH, such as hexadecanoic orpalmitic acid with n=14, heptadecanoic or margaric or daturic acid withn=15, octadecanoic or stearic acid with n=16, eicosanoic or arachidicacid with n=18, docosanoic or behenic acid with n=20, tetracosanoic orlignoceric acid with n=22, hexacosanoic or cerotic acid with n=24,heptacosanoic or carboceric acid with n=25, octacosanoic or montanicacid with n=26, triacontanoic or melissic acid with n=28,dotriacontanoic or lacceroic acid with n=30, tritriacontanoic orceromelissic or psyllic acid, with n=31, tetratriacontanoic or geddicacid with n=32, pentatriacontanoic or ceroplastic acid with n=33.Guerbet acids, characterized as 2,2-dialkyl ethanoic acids, are alsosuitable compounds. Preferred Guerbet acids include those containing 16to 36 carbons, many of which are commercially available from JarchemIndustries Inc., Newark, N.J. PRIPOL® 1009 (C-36 dimer acid mixtureincluding isomers of the formula

as well as other branched isomers which may include unsaturations andcyclic groups, available from Uniqema, New Castle, Del.; furtherinformation on C₃₆ dimer acids of this type is disclosed in, forexample, “Dimer Acids,” Kirk-Othmer Encyclopedia of Chemical Technology,Vol. 8, 4^(th) Ed. (1992), pp. 223 to 237, the disclosure of which istotally incorporated herein by reference) can also be used. Thesecarboxylic acids can be reacted with alcohols equipped with UV curablemoieties to form reactive esters. Examples of these alcohols include,but are not limited to, 2-allyloxyethanol from Sigma-Aldrich Co.;

TONE M-101 (R=H, n_(avg)=1), TONE M-100 (R=H, n_(avg)=2) and TONE M-201(R=Me, n_(avg)=1) from The Dow Chemical Company; and

CD572 (R=H, n=10) and SR604 (R=Me, n=4) from Sartomer Company, Inc.

The curable wax is preferably included in the ink in an amount of from,for example, about 15 to about 70% by weight of the ink, preferablyabout 20 to about 60% by weight of the ink, and more preferably fromabout 25 to about 50% by weight of the ink.

The curable monomer and curable wax together preferably form more than50% by weight of the ink, preferably at least 70% by weight of the ink,and more preferably at least 80% by weight of the ink. The weight ratioof curable monomer to curable wax may be, for example, from about 0.7:1to about 3:1, preferably from about 0.75:1 to about 2.5:1.

Any desired or effective colorant can be employed in the inks, includingdyes, pigments, mixtures thereof, and the like, provided that thecolorant can be dissolved or dispersed in the ink vehicle. Thecompositions can be used in combination with conventional ink colorantmaterials, such as Color Index (C.I.) Solvent Dyes, Disperse Dyes,modified Acid and Direct Dyes, Basic Dyes, Sulphur Dyes, Vat Dyes, andthe like.

Examples of suitable dyes include, but are not limited to, Eastmanolefin, Usharect Blue 86 (Direct Blue 86), available from Ushanti Color;Intralite Turquoise 8GL (Direct Blue 86), available from ClassicDyestuffs; Chemictive Brilliant Red 7BH (Reactive Red 4), available fromChemiequip; Levafix Black EB, available from Bayer; Reactron Red H8B(Reactive Red 31), available from Atlas Dye-Chem; D&C Red #28 (Acid Red92), available from Warner-Jenkinson; Direct Brilliant Pink B, availablefrom Global Colors; Acid Tartrazine, available from MetrochemIndustries; Cartasol Yellow 6GF Clariant; Carta Blue 2GL, available fromClariant; and the like. Particularly preferred are solvent dyes; withinthe class of solvent dyes, spirit soluble dyes are preferred because oftheir compatibility with the ink vehicles of the present invention.Examples of suitable spirit solvent dyes include Neozapon Red 492(BASF); Orasol Red G (Ciba); Direct Brilliant Pink B (Global Colors);Aizen Spilon Red C-BH (Hodogaya Chemical); Kayanol Red 3BL (NipponKayaku); Spirit Fast Yellow 3G; Aizen Spilon Yellow C-GNH (HodogayaChemical); Cartasol Brilliant Yellow 4GF (Clariant); Pergasol Yellow CGP(Ciba); Orasol Black RLP (Ciba); Savinyl Black RLS (Clariant); MorfastBlack Conc. A (Rohm and Haas); Orasol Blue GN (Ciba); Savinyl Blue GLS(Sandoz); Luxol Fast Blue MBSN (Pylam); Sevron Blue 5GMF (ClassicDyestuffs); Basacid Blue 750 (BASF), and the like. Neozapon Black X51[C.I. Solvent Black, C.I. 12195] (BASF), Sudan Blue 670 [C.I. 61554](BASF), Sudan Yellow 146 [C.I. 12700] (BASF), and Sudan Red 462 [C.I.260501] (BASF) are preferred.

Pigments are also suitable colorants for the inks. Examples of suitablepigments include, but are not limited to, Violet PALIOGEN Violet 5100(BASF); PALIOGEN Violet 5890 (BASF); HELIOGEN Green L8730 (BASF); LITHOLScarlet D3700 (BASF); Sunfast®Blue 15:4 (Sun Chemical 249-0592);Hostaperm Blue B2G-D (Clariant); Permanent Red P—F7RK; Hostaperm VioletBL (Clariant); LITHOL Scarlet 4440 (BASF); Bon Red C (Dominion ColorCompany); ORACET Pink RF (Ciba); PALIOGEN Red 3871 K (BASF);Sunfast®Blue 15:3 (Sun Chemical 249-1284); PALIOGEN Red 3340 (BASF);Sunfast®Carbazole Violet 23 (Sun Chemical 246-1670); LITHOL Fast ScarletL4300 (BASF); Sunbrite Yellow 17 (Sun Chemical 275-0023); HELIOGEN BlueL6900, L7020 (BASF); Sunbrite Yellow 74 (Sun Chemical 272-0558); SpectraPac® C Orange 16 (Sun Chemical 276-3016); HELIOGEN Blue K6902, K6910(BASF); Sunfast® Magenta 122 (Sun Chemical 228-0013); HELIOGEN BlueD6840, D7080 (BASF); Sudan Blue OS (BASF); NEOPEN Blue FF4012 (BASF); PVFast Blue B2GO1 (Clariant); IRGALITE Blue BCA (Ciba); PALIOGEN Blue 6470(BASF); Sudan Orange G (Aldrich), Sudan Orange 220 (BASF); PALIOGENOrange 3040 (BASF); PALIOGEN Yellow 152, 1560 (BASF); LITHOL Fast Yellow0991 K (BASF); PALIOTOL Yellow 1840 (BASF); NOVOPERM Yellow FGL(Clariant); Lumogen Yellow D0790 (BASF); Suco-Yellow L1250 (BASF);Suco-Yellow D1355 (BASF); Suco Fast Yellow D1 355, D1 351 (BASF);HOSTAPERM Pink E 02 (Clariant); Hansa Brilliant Yellow 5GX03 (Clariant);Permanent Yellow GRL 02 (Clariant); Permanent Rubine L6B 05 (Clariant);FANAL Pink D4830 (BASF); CINQUASIA Magenta (DU PONT), PALIOGEN BlackL0084 (BASF); Pigment Black K801 (BASF); and carbon blacks such as REGAL330™. (Cabot), Carbon Black 5250, Carbon Black 5750 (Columbia Chemical),mixtures thereof and the like.

The colorant is preferably included in the ink in an amount of from, forexample, about 0.1 to about 15% by weight of the ink, preferably about0.5 to about 6% by weight of the ink.

Radiation curable as used herein is intended to cover all forms ofcuring upon exposure to a radiation source, including light and heatsources and including in the presence or absence of initiators. Exampleradiation curing routes include, but are not limited to, curing usingultraviolet (UV) light, for example having a wavelength of 200-400 nm ormore rarely visible light, preferably in the presence of photoinitiatorsand/or sensitizers, curing using e-beam radiation, preferably in theabsence of photoinitiators, curing using thermal curing, in the presenceor absence of high temperature thermal initiators (and which arepreferably largely inactive at the jetting temperature), and appropriatecombinations thereof.

In embodiments, the composition further comprises an initiator,preferably a photoinitiator, that initiates polymerization of curablecomponents of the ink, including the curable monomer and the curablewax. The initiator should be soluble in the composition. In preferredembodiments, the initiator is a UV-activated photoinitiator.

In embodiments, the initiator is a radical initiator. Examples ofsuitable radical photoinitiators include, but are not limited to,ketones such as benzyl ketones, monomeric hydroxyl ketones, polymerichydroxyl ketones, and α-amino ketones; acyl phosphine oxides,metallocenes, benzophenones, such as 2,4,6-trimethylbenzophenone and4-methylbenzophenone; and thioxanthenones, such as2-isopropyl-9H-thioxanthen-9-one. A preferred ketone is1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one. In apreferred embodiment, the ink contains an α-amino ketone,1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one and2-isopropyl-9H-thioxanthen-9-one.

In other embodiments, the initiator is a cationic initiator. Examples ofsuitable cationic photoinitiators include, but are not limited to,aryldiazonium salts, diaryliodonium salts, triarysulfonium salts,triarylselenonium salts, dialkylphenacylsulfonium salts,triarylsulphoxonium salts and aryloxydiarylsulfonium salts.

The total amount of initiator included in the ink may be from, forexample, about 0.5 to about 15%, preferably from about 1 to about 10%,by weight of the ink.

In embodiments, the ink further comprises a curable oligomer. Suitablecurable oligomers include, but are not limited to, acrylated polyesters,acrylated polyethers, acrylated epoxies, urethane acrylates, andpentaerythritol tetraacrylate. Specific examples of suitable acrylatedoligomers include, but are not limited to, acrylated polyesteroligomers, such as CN2262 (Sartomer Co.), EB 812 (UCB Chemicals), CN2200(Sartomer Co.), CN2300 (Sartomer Co.), and the like, acrylated urethaneoligomers, such as EB270 (UCB Chemicals), EB 5129 (UCB Chemicals),CN2920 (Sartomer Co.), CN3211 (Sartomer Co.), and the like, acrylatedepoxy oligomers, such as EB 600 (UCB Chemicals), EB 3411 (UCBChemicals), CN2204 (Sartomer Co.), CN110 (Sartomer Co.), and the like;and pentaerythritol tetraacrylate oligomers, such as SR399LV (SartomerCo.) and the like.

The total amount of curable oligomer included in the ink may be from,for example, about 0.5 to about 15%, preferably from about 1 to about10%, by weight of the ink.

The ink may contain optional additives. Optional additives include, butare not limited to, surfactants, light stabilizers, UV absorbers, whichabsorb incident UV radiation and convert it to heat energy that isultimately dissipated, antioxidants, optical brighteners, which canimprove the appearance of the image and mask yellowing, thixotropicagents, dewetting agents, slip agents, foaming agents, antifoamingagents, flow agents, waxes, oils, plasticizers, binders, electricalconductive agents, fungicides, bactericides, organic and/or inorganicfiller particles, leveling agents, e.g., agents that create or reducedifferent gloss levels, opacifiers, antistatic agents, dispersants, andthe like. In particular, the composition may include, as a stabilizer, aradical scavenger, such as Irgastab UV 10 (Ciba Specialty Chemicals,Inc.). The composition may also include an inhibitor, preferably ahydroquinone, to stabilize the composition by prohibiting or, at least,delaying, polymerization of the oligomer and monomer components duringstorage, thus increasing the shelf life of the composition. However,additives may negatively affect cure rate, and thus care must be takenwhen formulating a composition using optional additives.

The total amount of other additives included in the ink may be from, forexample, about 0.5 to about 15%, preferably from about 1 to about 10%,by weight of the ink.

The inks described herein may be applied to a substrate to form animage. In embodiments, the method comprises providing a radiationcurable ink described herein at a first temperature; applying theradiation curable ink to the substrate to form an image, the substratebeing at a second temperature, which is below the first temperature; andexposing the radiation curable ink to radiation to cure the ink. Duringthe curing process, the curable monomer and the curable wax, optionallywith other curable components, such as the optional curable oligomer,are polymerized to form a cured image.

In a preferred embodiment, the composition is applied over the image byink jet printing. The inks described herein are preferably jetted attemperatures of about 50° C. to about 110° C., preferably about 60° C.to about 100° C. The jetting temperature must be within the range ofthermal stability of the composition, to prevent prematurepolymerization in the print head. At jetting, the inks preferably have aviscosity of from about 8 mPa-s to about 15 mPa-s, more preferably about10 mPa-s to about 12 mPa-s. The inks are thus ideally suited for use inpiezoelectric ink jet devices.

However, the substrate to which they are applied could be at atemperature at which the ink has a higher viscosity, such as a viscosityof from 10⁵ to 10⁷ mPa-s. For example, the substrate may be maintainedat a temperature of 50° C. or below, preferably from 0° C. to 50° C.,the temperature at the substrate being less than the jettingtemperature. Preferably, the substrate temperature is at least 10° C.below the first temperature. More preferably, the substrate temperatureis from 10 to 50° C. below the jetting temperature.

By jetting the ink at a temperature at which the ink is a liquid andhaving the substrate at the temperature at which the ink has a higherviscosity, a phase change can be provided. This phase change may preventthe composition from rapidly soaking into the substrate, avoiding or atleast minimizing showthrough. In addition, the substrate is exposed toradiation to initiate polymerization of the curable monomer, leading toa robust image.

The inks can be employed in apparatus for direct printing ink jetprocesses, wherein when droplets of the melted ink are ejected in animagewise pattern onto a recording substrate, the recording substrate isa final recording substrate. Alternatively, the inks can be employed inindirect (offset) printing ink jet applications, wherein when dropletsof the melted ink are ejected in an imagewise pattern onto a recordingsubstrate, the recording substrate is an intermediate transfer memberand the ink in the imagewise pattern is subsequently transferred fromthe intermediate transfer member to a final recording substrate.

The inks are suited for jetting onto an intermediate transfer substrate,e.g., an intermediate transfuse drum or belt. In a suitable design, theimage may be applied by jetting appropriately colored inks during fourto eighteen rotations (incremental movements) of the intermediatetransfuse member with respect to the ink jetting head, i.e., there is asmall translation of the printhead with respect to the substrate inbetween each rotation. This approach simplifies the printhead design,and the small movements ensure good droplet registration. Transfuse,i.e., a transfer and fusing step, is desirable in forming the image astransfuse enables a high quality image to be built up on a rapidlyrotating transfer member. This approach simplifies the printhead design,while the small movements of the head ensure good droplet registration.Transfuse typically involves jetting the ink from the ink jet head ontoan intermediate member such as a belt or drum, i.e., the transfusemember. This procedure allows the image to be rapidly built onto thetransfuse member for subsequent transfer and fusing to an imagereceiving substrate.

The intermediate transfer member may take any suitable form, although itis preferably a drum or belt. The member surface may be at roomtemperature, although in embodiments it is preferable to heat the membersuch that a surface temperature thereof is maintained within a narrowtemperature range so as to control the viscosity characteristics of theinks over a wide range of environmental conditions. This temperature ispreferably at or below the second temperature. In this way, the ink ismaintained on the surface of the transfer member until transfer to theimage receiving substrate.

Once upon the intermediate transfer member surface, the jetted ink maybe exposed to radiation to a limited extent so as to effect a limitedcuring of the ink upon the intermediate member surface. Thisintermediate curing is not to cure the ink to its full extent, butmerely to assist in setting the ink up so that it may be transferred tothe image receiving substrate with the appropriate amount ofpenetration, which requires the ink droplets to have a certain rheologybefore transfer. For controlling the extent of the curing if anintermediate cure is practiced, reference is made to Co-pendingapplication Ser. No. 11/034,850 filed Jan. 14, 2005, incorporated hereinby reference. This intermediate curing step may not be needed since thephase change is generally sufficient to impart the desired rheology tothe ink droplets.

Following jetting to the intermediate transfer member and optionalintermediate curing thereon, the ink is thereafter transferred to animage receiving substrate. The substrate may be any suitable materialsuch as paper, boxboard, cardboard, fabric, a transparency, plastic,glass, wood etc., although the ink is most preferably used in formingimages on paper. Following transfer to the substrate, the image on thesubstrate is exposed to radiation having an appropriate wavelength,mainly the wavelength at which the ink initiator absorbs radiation, toinitiate the curing reaction of the ink. The radiation exposure need notbe long, and may be for, e.g., about 0.05 to about 10 seconds, morepreferably from about 0.2 to about 5 seconds. These exposure times aremore often expressed as substrate speeds of the ink passing under a UVlamp. For example, the microwave energized, doped mercury bulbsavailable from UV Fusion (Gaithersburg, Md.) are placed in an ellipticalmirror assembly that is 10 cm wide; multiple units may be placed inseries. Thus, a belt speed of 0.1 ms⁻¹ would require 1 second for apoint of an image to pass under a single unit, while a belt speed 4.0ms⁻¹ would require 0.2 s to pass under four bulb assemblies. Theradiation to cure the polymerizable components of the ink is preferablyprovided by a variety of possible techniques, including but not limitedto a xenon lamp, laser light, D or H bulb, etc. The curing light may befiltered, if desired or necessary. The curable components of the inkreact to form a cured or crosslinked network of appropriate hardness.Preferably, the curing is substantially complete, i.e., at least 75% ofthe curable components are cured (polymerized and/or crosslinked), toallow the ink to be substantially hardened, and thereby to be much morescratch resistant, and also to adequately control the amount ofshowthrough on the substrate.

When an indirect printing process is used, the intermediate transfermember can be of any desired or suitable configuration, such as a drumor roller, a belt or web, a flat surface or platen, or the like. Theintermediate transfer member can be heated by any desired or suitablemethod, such as by situating heaters in or near the intermediatetransfer member, or the like. The intermediate transfer member may alsobe cooled by situating fans nearby or heat exchange with a cooled fluid.Optionally, a layer of a sacrificial liquid can be applied to theintermediate transfer member prior to ejecting the droplets of meltedink onto the intermediate transfer member, whereby the melted inkdroplets are ejected onto the sacrificial liquid layer on theintermediate transfer member, as disclosed in, for example, U.S. Pat.No. 5,389,958. Transfer from the intermediate transfer member to thefinal recording substrate can be by any desired or suitable method, suchas by passing the final recording substrate through a nip formed by theintermediate transfer member and a back member, which can be of anydesired or effective configuration, such as a drum or roller, a belt orweb, a flat surface or platen, or the like.

The present disclosure is also directed to a printer containing the inksdescribed herein. Specifically, the present disclosure relates to aprinter cartridge containing the inks described herein, as well as to aprinter containing the printer cartridge.

EXAMPLES

The following examples illustrate specific embodiments of the presentdisclosure. One skilled in the art would recognize that the appropriatereagents, component ratio/compositions may be adjusted as necessary toachieve specific product characteristics. All parts and percentages areby weight unless otherwise indicated.

Preparation of UNILIN 350 Acrylate

UNILIN 350 is a hydroxyl-terminated polyethylene wax available fromBaker-Petrolite (Sand Springs, Okla.). It has an M_(n) approximatelyequal to 375 g/mol.

UNILIN 350-acrylate is an acrylate-modified wax based on UNILIN 350.UNILIN 350-acrylate was prepared as follows: To a 2 L three neck flaskequipped with a reflux condenser, dropping funnel, thermometer, andDean-Stark trap was added UNILIN 350 (200 g, hydroxyl number 125.80 mgKOH/g, 80 wt %, obtained from Baker Petrolite, Tulsa, Okla.),p-toluenesulfonic acid (1.99 g, 0.8 wt %, obtained from Sigma-AldrichCo., Milwaukee, Wis.), hydroquinone (0.25 g, 0.1 wt %, obtained fromSigma-Aldrich Co., Milwaukee, Wis.) and toluene (600 mL). The reactionmixture was heated until dissolved. Acrylic acid (46 mL, 19 wt %) wasadded slowly by the addition funnel. The reaction was allowed to refluxuntil water ceased collecting in the Dean-Stark trap. Completion of thereaction was confirmed by ¹H NMR spectroscopy in toluene-d₈ (80° C.):the methylene protons adjacent to the hydroxyl group (δ3.38, t) wereconsumed and replaced by a series of triplets between δ4.27 and 3.97,representing RCH₂CH ₂OOCCH:CH₂. At the end of the reaction, the mixturewas cooled to room temperature and filtered. The solid was trituratedwith methanol, filtered, and dried in a vacuum oven. The toluenefiltrate was concentrated in vacuo, triturated with cold methanol,filtered, and dried in a vacuum oven. In total, 156 g of a yellow solid(broad mp ca. 50° C.) was recovered.

¹H NMR (300 MHz, toluene-d₈, 80° C.) δ 6.29-6.19 (1H, dd₁, J_(dd1)=17.3,1.7 Hz and dd₂, J_(dd2)=17.3, 1.7 Hz), 6.03-5.94 (1H, dd₁, J_(dd1)=17.3,10.4 Hz and dd₂, J_(dd2)=17.3, 10.4 Hz), 5.36-5.33 (1H, dd₁,J_(dd1)=10.4, 1.7 Hz and dd₂, J_(dd2)=10.4, 1.7 Hz), 4.27 (0.6H, t,J=6.5 Hz), 4.21 (0.3H, t, J=6.4 Hz), 4.06-3.96 (2.5H, t₁, J_(t1)=6.7 Hzand t₂, J_(t2)=6.7 Hz), 2.42-2.29 (0.9H, m), 2.28-2.16 (0.4H, m),1.65-1.43 (3.6H, m), 1.43-1.25 (104H, m), 0.91 (5.8H, t, J=6.5 Hz).

Examples 1-6

Inks 1-6 were made containing the components listed in Table 1.

TABLE 1 Ink Formulation (wt %) Component Function 1 2 3 4 5 6 Unilin 350acrylate wax Reactive wax; 48.4 39.6 29.7 29.7 29.7 29.7 phase changeagent SR9003 (propoxylated Reactive 40.7 49.5 59.4 54.4 54.4 54.4neopentyl glycol monomer diacrylate, a low viscosity monomer fromSartomer Company, Inc.) CN2262 (polyester Reactive — — — 5.0 — —acrylate oligomer from oligomers Sartomer Company, Inc.) SR399LV — — — —5.0 — (dipentaerythritol pentaacrylate ester from Sartomer Company,Inc.) EB 812 (acrylated — — — — — 5.0 polyester oligomer from UCBChemicals) Irgacure 379 (α-amino Photoinitiators 2.9 2.9 2.9 2.9 2.9 2.9ketone photoinitiator from Ciba Specialty Chemicals, Inc.) Irgacure 29591-[4-(2- 2.9 2.9 2.9 2.9 2.9 2.9 hydroxyethoxy)- phenyl]-2-hydroxy-2-methyl-1-propane-1-one from Ciba Specialty Chemicals, Inc.) Darocur ITX1.9 1.9 1.9 1.9 1.9 1.9 (2-isopropyl- 9H-thioxanthen-9-one from CibaSpecialty Chemicals, Inc.) Irgastab UV 10 (a Stabilizer 0.2 0.2 0.2 0.20.2 0.2 radical scavenger from Ciba Specialty Chemicals, Inc.) Eastmanred-magenta Colorant 3.0 3.0 3.0 3.0 3.0 3.0 olefin dye

The inks were formulated as follows: The reactive wax (prefiltered to 2μm), monomer, oligomer (optional), photoinitiators and stabilizer wereheated to 100° C. with stirring. After 30 min at this temperature, thecolorant was added and the resulting ink was stirred for 1 h longer.Each ink was pipetted onto a glass slide as a liquid at 100° C. andexposed to UV light from a UV Fusion LC-6B Benchtop Conveyor equippedwith UV Fusion F300S Ultraviolet Lamp System employing a “D” bulb forabout 5 s. The cured samples were heated at 100° C. for 30 min and didnot completely remelt, indicating that polymerization had occurred.

Ink 1 was filtered to 2 μm and jetted onto three different types ofpaper: Xerox Digital Colour Gloss (80 lb), International PaperHammermill Laser Print (24 lb) and Xerox Premium Multipurpose 4024 (24lb). No showthrough was observed on the Gloss and Hammermill papers andshowthrough was minimal on the 4024 paper. If prints were left uncuredovernight, ink began to soak through the Hammermill and 4024 papers,indicating the ink had formed a robust polymer after exposure to UVlight.

The rheological profiles of these inks are depicted in the FIGURE. Theviscosities were measured on a Rheometrics Fluid Spectrometer RFS3 withcone and plate geometry equipped with a Peltier plate at a frequency of1 Hz.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also,various presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art, and are also intended to beencompassed by the following claims.

1. A radiation curable ink comprising: a curable monomer that is liquidat 25° C., a curable wax, and a colorant, wherein the ink has aviscosity of from about 10⁵ cP to about 10⁷ cP at a temperature of about50° C. or below, wherein the curable wax is a hydroxyl-terminatedpolyethylene wax functionalized with at least one curable group selectedfrom the group consisting of a methacrylate, alkene, allylic ether,epoxide and oxetane, or a carboxylic acid-terminated polyethylene waxfunctionalized with at least one curable group selected from the groupconsisting of a methacrylate, alkene, allylic ether, epoxide andoxetane, wherein the hydroxyl-terminated polyethylene wax is of theformula CH₃—(CH₂)_(n)—CH₂OH, where n is from about 16 to about 50, andwherein the carboxylic acid-terminated polyethylene wax is of theformula CH₃—(CH₂)_(n)—COOH, where n is from 14 to about
 50. 2. Aradiation curable ink according to claim 1, wherein the ink furthercomprises at least one radiation-activated initiator that initiatespolymerization of the curable monomer and the curable wax.
 3. Theradiation curable ink according to claim 1, wherein the curable monomerhas a viscosity of no more than 15 cP at 25° C.
 4. The radiation curableink according to claim 1, wherein the ink has a viscosity of from about8 cP to about 15 cP at a temperature from about 60° C. to about 100° C.5. The radiation curable ink according to claim 1, wherein the ink has aviscosity of from about 10⁵ cP to about 10⁷ cP at a temperature fromabout 0° C. to about 50° C.
 6. The radiation curable ink according toclaim 1, wherein the ink further comprises curable oligomer.
 7. Theradiation curable ink according to claim 1, wherein the ink furthercomprises a stabilizer.
 8. The radiation curable ink according to claim2, wherein the radiation-activated initiator radically initiatespolymerization of the curable monomer and the curable wax.
 9. Theradiation curable ink according to claim 2, wherein theradiation-activated initiator is activated by ultra-violet light. 10.The radiation curable ink according to claim 1, wherein the curablemonomer contains at least one reactive moiety selected from the groupconsisting of acrylate, methacrylate, alkene and allylic ether.
 11. Theradiation curable ink according to claim 2, wherein the at least oneradiation-activated initiator is a photoinitiator selected from thegroup consisting of benzyl ketones, monomeric hydroxyl ketones,polymeric hydroxyl ketones, a-amino ketones, acyl phosphine oxides,metallocenes, benzophenone, benzophenone derivatives and isopropylthioxanthenones.
 12. The radiation curable ink according to claim 7,wherein the stabilizer is a radical scavenger.
 13. A printer cartridgecomprising radiation curable ink according to claim
 1. 14. A printercomprising a printer cartridge according to claim 13.